We are using the chemostat for studying the effect of changes in growth condition on the surface components and extracellular products, particularly lipoteichoic acid, of cariogenic bacteria; changes being followed by chemical, serological and microscopic procedures. The organisms chosen are representative strains of streptococci, lactobacilli and actinomycetes, with studies initially concentrating on those strains whose cell wall carbohydrates--polysaccharides or teichoic acids--have been sufficiently characterized. These surface components are of importance in a) the identification of a particular organism and b) defining the nature of the organism's interaction with the environment. Lipoteichoic acid is a recognized component of the membrane of most gram-positive bacteria but it may also occur extracellularly in significant amounts. The bacterial cell surface is particularly sensitive to changes in growth conditions Thus, by obtaining a clearer understanding of the effect of environmental conditions on the growth of cariogenic bacteria, we can better understand their role in inducing caries.